The present invention relates to a process for preparing organosilicon compounds by the silylation of conjugated dienes and more particularly, to the process for preparing organosilicon compounds expressed by the following formulas 1a and 1b in high yield, comprising the steps of heating trichlorosilane in the presence of quaternary organophosphonium salt catalyst to generate dichlorosilylene (:SiCl2); and silylating the result with linear or cyclic conjugated dienes, 
wherein R1, R2, R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl or phenyl group, or two functional groups among R1, R2, R3, R4, R5 and R6 may be covalently bonded to form a cyclic compound of C4-C8.
Organosilicon compounds have been widely used as useful starting materials for silicons. Especially, cyclic silicon compounds have become essential monomer precursors in the production of inorganic polymers by ring-opening polymerization. Further, they serve an important role in investigating the mechanisms of silicon chemistry. Therefore, researches in cyclic silicon compounds have been highly increased. By the 1980s, the only possible way of synthesizing the cyclic silicon compounds was through silylene (:Si). In 1978, Chernyshev of Russia reported the preparation of silylenes by the pyrolysis of hexachlorodisilane However, hexachlorodisilane is s are not suitable as a silylene precursors, because it would be too costly to be utilized on a large scale in industry [E. A. Chernyshev, N. G. Komalenkiva, S. A. Bashkirova and Sokolov, Zh Obshch. Kihm., 1978, 48, 830]. Since then, extensive researches have been developed by Gaspar of the US. Alternative processes for preparing cyclic silicon compounds are taught by Weber of the US introducing a two-step process with the dichloro allylic compound as a starting material [Robert Damrauer, Roger Simonm Andre Laporterie, Georges Manuel, Young Tae Park and William P. Weber, J. Organomet. Chem., 1990, 391, 7-12]. 
Although this method is still in use, it has some disadvantages that the reaction time is long; the isolation and purification are difficult; and this method is not applicable for other conjugated dienes.
The currently known methods for preparing cyclic silicon compounds are synthesizing mainly cyclic organic silanes by pyrolysis or photoreaction using costly disilanes at a high temperature or by using trichlorosilane and trialkylamine, followed by a Grignard reaction. However, these methods are not only limited in preparing a variety of cyclic silicon compounds, but also difficult to obtain good yield.
The present inventors have discovered a method of preparing a variety of organosilicon compounds by the dehydrohalogenation of alkyl halides and chlorosilanes in the presence of quaternary organophosphonium salt catalyst [U.S. Pat. Nos. 6,251,067 and 6,392,077]. It was noticed that a small amount of double silylated product was formed at the double bond of an allyl group with dehydrohologenation of allyl chloride or methyl allyl chloride. In the process of investigating the reaction condition to produce such double silylated product, we found that double silylation proceeds at the unsaturated organic compound due to the generation of silylene, when the reaction is carried at a higher temperature than that of the conventional dehydrohalogenation. The present invention was completed by identifying that cyclized organosilanes as a major product and double silylated compounds as a byproduct are obtained by the reaction of various conjugated dienes and silanes having Sixe2x80x94H bonds.
According to the above-mentioned prior arts, cyclic organosilicon compounds are prepared by the pyrolysis of conjugated dienes and disilanes at a high temperature, or by employing amines and simultaneous Grignard reaction. However, the coupling reaction between conjugated dienes and disilanes requires the use of costly disilanes which is further difficult to handle due to its instability, thus being inappropriate to be utilized for industrial purposes. Additionally, in the method employing amines, the ammonium salt is produced by the neutralization of hydrogen chloride generated during the reaction with amine, and in the Grignard reaction, a large amount of solvent has to be used, and the separation and treatment of the salt generated during the reaction with magnesium require a large cost.
Therefore, it would be also too costly to be utilized on a large scale in industry.
On the contrary, the process for preparing organosilicons according to this invention provides distinguished advantages: (1) the process is much more simple than that using the disilane compound; (2) trichlorosilane, which is much cheaper and industrially available, is used as a raw material; (3) the cyclic silicon compounds can be obtained with good yield because trichlorosilane can form dichlorosilylene (:SiCl2) even at a low temperature in the presence of a small amount of quaternary organophosphonium salt; and (4) the catalyst can be easily recovered from the reaction medium and maintains good catalytic activity with recycles.
Accordingly, an object of this invention is to provide an economical and effective method for preparing organosilicon compounds.
The present invention relates to a process for preparing the organosilicon compounds expressed by the following formulas 1a and 1b by the silylation of trichlorosilane (HSiCl3) and conjugated diene organic compound expressed by the following formula 2 in the presence of quaternary organophosphonium salt catalyst, 
wherein R1, R2, R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl or phenyl, or two functional groups among R1, R2, R3, R4, R5 and R6 may be covalently bonded to form a cyclic compound of C4-C8.
Hereunder is given a more detailed description.
This invention relates to a process for preparing the organosilicon compounds of formulas 1a and 1b by the silylation of trichlorosilanes and conjugated dienes with various structures in the presence of quaternary organophosphonium salt catalyst.
The process for preparing such various cyclic silicon compounds has never been reported before.
To improve disadvantages associated with the conventional processes, the inventors have directed to find effective catalysts which are economically feasible in the process for preparing organic silanes for a large scale in industry. So, the inventors used trichlorosilane as a starting material, which is relatively cheap, and a small amount of quaternary organophosphonium salt as a catalyst. The coupling reaction of the present invention is carried out at a temperature of 150-180xc2x0 C. to give excellent yields. The catalyst could be easily recovered for recycle which makes the process more economical for industrial use.
The process for preparing organosilicon compounds by the silylation of conjugated dienes is described as follows.
First, trichlorosilane, conjugated dienes and quaternary organophosphonium salt are placed all together into a reaction tube which is stable at a high temperature and a high pressure (e.g., a stainless steel tube). After sealing the reaction tube with a stopper, heating and stirring may be applied to obtain organosilicon compounds of formulas 1a and 1b.
The conjugated dienes, raw material of this invention, can be expressed by the following formula 2, 
wherein R1, R2, R3, R4, R5 and R6 are the same as defined above.
Examples of the conjugated dienes of formula 2 include 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3butadiene, 1,4diphenyl-1,3-butadiene, cyclopentadiene, cyclohexadiene, cycloheptadiene, cyclooctadiene and anthracene.
Quaternary organophosphonium salt, the catalyst of this invention, is effective in the silylation of conjugated dienes and trichlorosilane having a Sixe2x80x94H bond. Quaternary organophosphonium salt can be expressed by the following formula 3,
(Rxe2x80x2)4PXxe2x80x83xe2x80x83(3)
wherein X is a halogen atom; Rxe2x80x2 is independently C1-C9 alkyl, phenyl group, xe2x80x94(CH2)nxe2x80x94C6H5 (n is an integer of 0-6), or two Rxe2x80x2 can be covalently bonded to each other to form a cyclic compound of C4-C8.
Specific examples of the quaternary organophosphonium salt include benzyltributylphosphonium chloride, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, tetramethylphosphonium bromide, tetraethylphosphonium chloride, (4-ethylbenzyl)triphenylphosphonium chloride, hexyltriphenylphosphonium chloride, benzyltriphenylphosphonium chloride and tetraphenylphosphonium chloride. The quaternary organophosphonium salt catalyst can be easily recovered from the reaction medium. For example, when the reaction product is placed under vacuum-distillation upon completion of the reaction, the remaining catalyst can be easily recovered. The recovery ratio can be as high as 80%. The recovered catalyst can be recrystallized from the solvent for recycle.
When the reaction mixture is heated in the presence of the quaternary organophosphonium salt catalyst, trichlorosilane is degraded to form dichlorosilylene (:SiCl2) which reacts with conjugated dienes to give the organosilicon compounds expressed by formulas 1a and 1b. For 1 mol of conjugated dienes, 1-8 mol of trichlorosilane is used; and 0.01-1 mol, preferably 0.05-0.15 mol, of quaternary organophosphonium salt catalyst is used. There is no need to add a reaction solvent. If required, aromatic hydrocarbon may be used as the reaction solvent. The reaction is performed at 10-250xc2x0 C., preferably at 100-200xc2x0 C., for 1-48 hours. When the reaction is completed, the target compound can be obtained by distilling the reaction mixture under normal or reduced pressure.
As explained above, the present invention provides a method of preparing organosilicon compounds with good yield by the silylation of various conjugated dienes and trichlorosilanes having Sixe2x80x94H bonds in the presence of quaternary organophosphonium salt. This method uses a small amount of catalyst, which can be easily recovered for recycle and has good catalytic activity even at a low temperature. Considering these advantages, the present invention is a very economical and effective method, which can be used for the preparation of various and new organosilicon compounds. Furthermore, its process is very simple and the production cost is relatively low. The organosilicon compounds prepared by this invention can be widely used for the synthesis of various polymers.